Flexible electronics is aimed to be portable, lightweight, bendable, foldable, twistable, and even wearable. Due to these features, the corresponding power sources should be lightweight and stable under different mechanical deformation conditions. Recently, much progress has been made in the development of flexible all-solid-state supercapacitors for flexible electronics owing to their ease of handing, small size, and safety. The main limitations, however, are their low volumetric energy density and limited mechanical durability. A typical fabrication procedure of an all-solid-state supercapacitor includes the synthesis of active materials on a conductive and flexible substrate, followed by assembly into devices using a gel electrolyte. However, little emphasis has been placed on the development of free-standing flexible active materials without the need for extra support, which is vital for the improvement of energy and power densities based on the volume of the whole devices. In this respect, some progress has been made in the design of graphene-based film electrodes for all-solid-state supercapacitors. Carbon nanotube architectures have also been successfully designed as a mechanical support to develop fiber type supercapacitors with superior mechanical durability. In spite of this progress, the energy density of the devices is still limited by the use of flexible but inert substrates or the large proportion of the low-specific-capacitance carbon nanotubes. In other words, an ideal electrode material for flexible all-solid-state supercapacitors should possess high specific capacitance and be highly flexible by itself without the need for mechanical support. However, to date, there are very few successful examples of such all-solid-state supercapacitors showing stable electrochemical performances under continuous dynamic mechanical deformation.
What is needed is a flexible free-standing all-solid-state supercapacitor for flexible electronics.